Hormonal and metabolic regulation of hepatic ketogenesis will be studied in isolated rat hepatocytes. The primary objective is to determine more precisely the quantitative antiketogenic action of insulin and the ketogenic action of glucagon in the liver. A second objective is to define more precisely the quantitative antiketogenic actions of various antiketogenic metabolites (glucose, lactate, etc.). A major postulate of this study is that the overall supply of carbohydrate available to the liver either as glycogen within the tissue, or gluconeogenic precursors, e.g. lactate, alanine, available to the liver influences the quantitative changes induced in ketogenic rates by insulin and glucagon. We will examine this possibility by studying the influence of varying doses of glucagon and insulin in vitro on ketogenesis in isolated liver cells containing varying amounts of glycogen, and in cells incubated with media containing varying amounts of gluconeogenic substrates. The second major phase of these proposed studies involves studies in the mechanism of hormonal regulation of ketogenesis. We propose to evaluate the possible role of peroxisomes (microbodies) and the important constituent enzymes of this organelle, catalase and peroxidase, in the regulation of ketogenesis. Certain evidence suggests that these enzymes may be involved in the regulation of hepatic lipid metabolism and ketogenesis. Drugs will be used to manipulate the number of peroxisomes and catalase and peroxidase activity. The consequential effects of these alterations on rates of ketogenesis in isolated hepatocytes will be examined. The drug, clofibrate, will be utilized to increase peroxisomes, and catalase, and possibly peroxidase activity, while the drug allylisopropylacetamide (AIA) will be utilized to decrease activities of these enzymes. We also propose to study ketogenesis in isolated hepatocytes in "acatalasemic" mice which are reported to have low catalase and possible increased peroxidase activity. We will also investigate the possible role of the carnitine acyltransferase pathway in the regulation of hepatic ketogenesis.